1. Field of the Invention
The present invention relates to a method of continuously manufacturing a row of helically coiled or zigzag coupling elements for a slide fastener which are made of thermoplastic filamentary material.
2. Prior Art
There has heretofore been practiced a method of manufacturing a row of helically coiled slide fastener coupling elements as disclosed in U.S. Pat. No. 3,984,970 (Terada et al), patented Oct. 12, 1976. According to the disclosed method, a thermoplastic filament is slackened before it continuously enters a coiling device, an adjustable weight is suspended from the slackened portion of the filament, and the adjustable weight is adjusted to maintain the filament under desired tensioning forces.
It is known that as the filament, while it is being coiled around a mandrel, is kept under greater tension, the helically coiled coupling elements thus fabricated have smaller dimensions, that is, the length and width of coupling element legs, and conversely, as the filament undergoes smaller tension, the formed coupling elements have larger dimensions. Therefore, the dimensions of coupling elements can be changed as desired by adjusting the weight by which the element-forming filament is tensioned. The above principle holds true for the manufacture of meandering or zigzag coupling elements.
With the conventional method, the dimensions of the coupling elements that are manufactured are measured by the operator with a gage at suitable intervals of time, and the filament tension is varied by selectively adding or removing weights on the basis of the measurements. The gaging and weight adjusting processes have heretofore been tedious and time-consuming. It has also been unable to make coupling elements of uniform dimensions and shapes for the following reasons: The filament is made of synthetic resin such, for example, as nylon or polyester, and hence its properties, such as elongation, tend to change due to variations in environmental conditions such as temperature and humidity. Before being formed into continuous coupling elements, the filament is stored on a large-size bobbin. The filament properties are liable to vary at radially inward and outward positions or upper and lower positions on the filament wound around the bobbin, dependent on the amount of filament and the conditions under which the bobbin is mounted. Therefore, the filament as it is unwound from the bobbin varies in property from position to position on the filament. The filament is subject to continuous property variations while it is being continuously supplied to a coiling machine. The prior method has been unable to adjust the filament tension in a manner to cancel out such continuous property changes of the filament prior to the coiling thereof, with the result that the coupling elements as formed suffer from varying dimensions and shapes, which will prevent smooth intermeshing engagement of a pair of companion rows of coupling elements that are manufactured.